In recent years, there has been developed a biometric authentication technique in which, on the basis of a biological image expressing biological information such as the pattern of the vein of a hand or a finger, a fingerprint, a palm print, or the like, the user of a device or a system is authenticated. For example, a biometric authentication device utilizing such a biometric authentication technique acquires, as an input biological image, a biological image expressing the biological information of a user that intends to use the biometric authentication device. In addition, the biometric authentication device matches the input biological information of the user, expressed in the input biological image, against registration biological information serving as biological information expressed in the preliminarily registered biological image of a registered user. When, on the basis of the result of the matching processing, having determined that the input biological information matches the registration biological information, the biometric authentication device authenticates the user as a registered user having a valid authority. In addition, the biometric authentication device allows the authenticated user to use a device, into which the biometric authentication device is incorporated, or another device connected to the biometric authentication device.
In order to enhance authentication accuracy, it is desirable that the direction of the input biological information on the input biological image is headed in a preliminarily defined direction and a region including the biological information is adequately disposed with respect to a sensor so the whole input biological information is captured in the input biological image. Therefore, for example, in Japanese Laid-open Patent Publication No. 2000-268174 or International Publication Pamphlet No. WO 2004/21884, there has been disclosed a technique in which a guide used for adequately disposing a region including biological information is provided. In addition, in International Publication Pamphlet No. WO 2004/21884, there has been disclosed a technique in which, from an image in which a region including biological information is captured, the position or direction of the region is detected and when it is inadequate to correct the image of the biological information on the basis of the detected position or direction, a user is notified of that effect. Furthermore, in Japanese Laid-open Patent Publication No. 2007-58643, there has been disclosed a finger vein pattern input device that includes a finger tip portion rest, equipped with a fingertip guide, and a finger base portion rest and in which the finger tip portion rest is slidable in the direction of the finger base portion rest along the internal wall surface of a main body. When a user has moved a finger along with the finger tip portion rest and hence the finger has reached an adequate position, this finger vein pattern input device takes an image of the vein pattern of the finger.